Tek-Tips is the largest IT community on the Internet today!

Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!

Register Log in
  • Congratulations cowski on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Tensile vs. Compressive Modulus % Difference

Status
Not open for further replies.
Ryan_aero

Ryan_aero

Aerospace
Joined
Mar 6, 2020
Messages
15
Location
US
What is the typical % difference between tensile/compressive modulus for the widely used carbon fiber material systems?

I've seen values ranging from 0 to 30% from literature and internal M&P test efforts. I understand it can be a difficult parameter to measure and want to understand what is typical.

Additionally, does it make sense to generate compressive modulus value using sandwich coupons if nearly all our practical structures are of sandwich construction?

Appreciate the feedback

Ryan
 
Sort by date Sort by votes
About 10% difference is typical. There is lots of lamina data available in CMH-17 Volume 2 (available at sae.org).

Compression modulus is not difficult to measure, though generally requires use of strain gages due to short gage lengths required to prevent specimen buckling.

Are the facesheets of your sandwich panels precured or cocured? do the panels use honeycomb core? Both tension and compression moduli will be reduced for sandwich panel facesheets that are cocured over honeycomb core where the facesheet dimples into the cells.

 
Upvote 0 Downvote
Awesome - that's super helpful. It sounds like there is a good chance some of our coupons are buckling if we are measuring 20-30% knockdowns. I'll circle back with our M&P team to try to confirm that.

The sandwich panel facesheets would be cocured to either honeycomb or foam.
 
Upvote 0 Downvote
For carbon fiber composites, modulus should be calculated as secant value over 0.001 to 0.004 in/in strain range, so should be well below onset of buckling (unless the specimen/fixture is complete junk).

Ask them for the load-strain plots for both tension and compression tests.
 
Upvote 0 Downvote
This reminds me of the time I was asked to get involved in helping solve a mystery as to why a new material was not performing well in compression. It turned out that the compression test fixture used linear ball bushings on 0.5 inch rods to keep the two halves in alignment during the test. No one noticed that the bushings had been pushed up into their mounting holes so that there was little engagement between the bushings and guide rods. Thus the two halves of the test fixture were not staying perfectly aligned during testing, leading to low compression numbers.
 
Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

O.Rezzik
  • Locked
  • Question Question
FGM tensile strength test pieces dimensions standards or norms.
Replies
0
Views
643
O.Rezzik
O.Rezzik
Burner2k
  • Locked
  • Question Question
Young's Modulus & Shear Modulus Calculation
Replies
2
Views
1K
SWComposites
SWComposites
vinguy
  • Locked
  • Question Question
Compressed Air vs Nitrogen for Autoclave Cures
Replies
5
Views
2K
georgeverghese
georgeverghese
midsidenode
  • Locked
  • Question Question
Film Adhesive - Supported vs Unsupported
Replies
3
Views
1K
SWComposites
SWComposites
Sean99
  • Locked
  • Question Question
Aluminum plate welded to aluminum plate section modulus
Replies
6
Views
644
Ng2020
Ng2020

Part and Inventory Search

Sponsor

Back
Top